Impact tool mechanism



Sept. 24, 1946; c. H; RICHARDS IMPACT TOOL MECHANISM Filed Feb. 24, 1944.3 Sheets-Sheet l aw i iifg P 1946- c. H. RICVHARDS 2,408,228

IMPACT TOOL MECHANI SM Filed Feb. 24, 1944 3 Sheets-Sheet 2 v 1NVENTOR.'{864M 21k, M d-f A Sept. 24, 1946- c. H. RICHARDS IMPACT TOOL MECHANISMa Sheets-Sheet s Filed Feb. 24', 1944 INVEN'I'Q ii: 4 44 [624mm PatentedSept. 24, 1946 UNITED STATES PATENT-i FFICE,

I Carroll H. Richards, Boston, Mass. I v Application February 24, 1944,Serial No. 523,694

This invention relates to impact tool mechanisms, such as impactwrenches.

6 Claims. (oi-192 305) .witliparts of the motor and ho us ing brokenaway.

In previous impact mechanisms with which I have been familiar, thehammer is decelerated on impact with the driven element. In themechanism of the invention, a rotating hammer is accelerated and iscapable of delivering a, greater driving force to the driven member.This is a great advantage because it provides greater force when neededmost. v

The deceleration of the impact hammer in previous impact tool mechanismsnecessarily causes the motor driving the mechanism to slow down, orstop, between impacts, and heretofore the only motor that would performsatisfactorily under these conditions has been 'a pneumatic orcompressed-air motor. An impact tool embodying the present invention,however, is capable of being driven by an electric motor, as Well as bycompressed air. This is a great advantage'in operations where compresedair is not readily available.

Furthermore, in prior impact tool mechanisms the hammer surface becomesquickly distorted and deformed through constant hammering, and.

the same angle of contact between the hammer and anvil faces at alltimes is impossible. These machines vary in performance, quickly losetheir efficiency, and parts must be frequently replaced.

In my mechanism, however, positive means are provided for maintainingthe same angle of impact at all times for greatest efiiciency andconstant performance, despite wear. r

A further important object of the present invention is to provide animpact tool mechanism which will absorb the reaction of the impactwithin itself.

Another advantage of the present tool lies in the provision of auxiliarymeans to dampen or smooth out the revolutions of the mechanism to reducevibration and jerkiness in operation.

Before explaining in detail the present invention it is to be understoodthat the invention is not limited in its application to the details ofconstruction and arrangement of parts illustrated in the accompanyingdrawings, since the invention is capable of otherembodiments and ofbeing practiced or carried out in various ways. Also it is to beunderstood that the phraseology or terminology employed herein is forthe purpose of description and not of limitation, and it is not intendedto limit the invention claimed herein beyond the requirements of theprior art.

In the drawings: r Fig. 1 is a sectional view of an impact wrench,

of Fig. w r

Fig; .3 is asectional view taken on line 3 -3 ofFig.1.

"Fig. 3a is' a detail end view, of the rotatable torque receiving memberD, shown in'Figs. 1,.2

and3. 1 1,, Fig- 4.is a sectional view of another form of constructionof the rotatable torque receiving member with partof itshousing andother parts broken away. V

Fig. 5 is an end view of the rotatable torque receiving member shown inFig. 4. q I

. Fig. 6 is a, section of the rotatable torque re- .ceiving member takenon line 66 of Fig. i.

Fig. 7 is a, plan view'of one of the parts of the rotatable torquereceiving member shown in Fig. 4. Fig. 8 isa side elevation of thedriving element. Fig-9 is a side elevation of the driven element. Fig.10 is a perspective view of the driving connection between the rotatabletorque receiving member and the driven element. I I q Fig. 11 is aperspective view of a special gear constitutingthe driving connectionbetween the rotatable torque receiving member and the driving element. y

Figs. 12 to 19 inclusive are diagrams showing the relation of'certainof, the parts at difierent periods in the operation of the device, takenfrom Fig. 2 is arsectionalview taken on line 2-2 the point of view ofthe operator using the deof Fig. 1, and opposite to anism of theinvention which housing is made in two parts, upper part B and lowerpart K, conventionally fitted'together and held in place by bolts andnuts 40 .(Fig. 1). Spindle A of the driving power unit is journaled inball bearing l0 conventionally held in partition ll located in the upperportion Bof the housing. It is understoodthata suitable motor,pneumatic, electric, or otherwise (not shown), provides power fordriving spindle A. The splined end [2 of spindle A fits into splinedhole l3 of the driving element C, and the driving force is transmittedby spindle A through these splines to the driving element C. The end I4of driving element C abuts one end of ball bearing l0 and aids inlocating the ball bearing. Driving element C (Figs. 1, 2 and 8) includesthe flanged portions I 5, having two gear teeth 7 spaces It therein andextending from the center 3 shaft portion 11, at the extreme end ofwhich is another shaft portion l8, smaller in diameter than portion IT.

A rotatable torque receiving member D (Figs. 1, 3 and 3a) is rotatablymounted on driving element C about shaft portion 11, having a centralhole [9 into which shaft portion l1 fits.

Two driving connections E (Figs. 1, 2 and 10) having shaft portions arerotatably mounted in holes or bearings 29 and 30 of the rotatable torquereceiving member D (Figs. 1 and 3a), said holes 29 and 36 being locateda, suitable distance out from the center of the rotatabletorquereceiving member D. Shaft portion 20 has splines 2| at one end,and an annular groove 22 adjacent the splines 21 adapted toreceive aconventional spring fastening ring 32 (Fig. l). Splined on the splinedends of driving connection-E are specially designed acceleration controlparts H.(Figs. 1, 2 and 11), each having one tooth 3i. Gear teeth 3ioperate in gearspaces l6 of driving element C and receive the drivingforce therefrom. The contacting surfaces of these gear teeth 3| arearcuate surfaces and their radius R (Fig. 2) may be changed to suitdifferent operating conditions. The spring rings 32 fitting in theannular grooves 22 on splined ends 2! of driv ing connection E aid inlocating parts. H on the splined end 2! of shaft portion 20 and preventlongitudinal movement of the parts H in one direction along shaftportion 20.

At the opposite end of shaft portion 2%! of driving co nection E. andintegral with it. is hammer head F (Figs. 1, 3 and 10), having hammerfaces 23 and 24 forming a V, the open ends of the V terminating inrounded noses 25 and 26 adapted to contact a cylindrical surface guide(3%). The V-shaped hammer faces facilitate the transmission of the drivein either direction. Cylindrical surface portions 21 and 28, oppositerounded noses 25 and 25 respectively, on hammer head F slidably contactinner cylindrical surface 55 of guide ring G (Figs. 1 and. 3), andmaintain the proper angle of impact for hammer faces 23 and 24 at alltimes. Guide ring G is suitably located and fastened in the lowerportion K of the housing.

Driven element I (Figs. 1', 3 and 9) is rotatably mounted in bearing 33located and held in lower portion K of the housing. Cylindrical endportion 34 of driven element I, having central cavity 36 therein,receives the smaller shaft portion l8 of the driving element C, andserves as a bearing for shaft portion l8, and as a lubricant reservoir.Cylindrical end portion 34 has two anvil faces of inverted V-shape.oppositely located thereon. adapted to receive the impact of hammerfaces 23 and 24 of hammer head F (Fig. 3)., and to drive driven elementI in either direction around shaft portion l8 of driving element C.Rounded noses 25 and 23 of the hammer heads F on the driving connectionsE, ride the cylindrical surface 34 of driven element I when notcontacting the anvil faces 35 and aid in guiding hammer heads F ofdriving connection E, to insure the correct angle of impact atfthe exactinstant of impact of hammer faces 23 and 24, with the cooperating anvilfaces 35 of driven element I.

menjtC, in driving contact itransmits the drive to the socket or wrench3'3 which is adapted to receive bolt heads, nuts, studs, or otherresisting element to be turned.

The operation of my device is as follows: After fitting the socket orwrench 33 over the bolt or other head to be tightened, the motor isstarted and this rotates in a clockwise direction, as viewed from theleft, the position of the operator using the wrench (Fig. l). Spindle A'of the motor which has splined driving connection with driving element0, imparts the drive to driving element (3. The surfaces of gear teethspaces it of driving elewith gear teeth if of parts Hin turn transmitthe drive to the parts I i, Whichbeing splined to end 2! of the drivingcon: nections E, transmit the drive thereto, and thence to hammer headsF,-which are integral parts of driving connections E.

Assuming that the parts are in the positions shown in FigalS and 3.9,the hammer heads F and the torque balancer D rotate a whole with thedriving element C andat the speed of the "drive, until the hammer faces23of hammer heads F. contact the cooperatinganvil faces of the drivenelement I.

After the hammer faces 23 have made contact with the cooperative anvilfaces 35, if the ratio of the driving torque transmitted through thehammer faces 23 to the anvil faces35, to the resisting torquetransmitted at the anvil faces 35 from driven element L is substantiallythe same, then the driving element C, the rotatable torque receivingmemberD, parts H, driving connections E, and the driven element I, willall rotate as 'a whole at the same speed as the driving element C, withsubstantially no relative movement between the parts moving as a whole(Figs. 12 and 13).

v However, if after the hammer faces 23 have made contact with the anvilfaces 35 and driving torque transmitted through the hammer faces 23 tothe. anvil faces 35 is less than the resisting torque transmitted to theanvil face-s 35 from the driven element I, the operation then is asfollows: The rotatable torque receiving member D re sponds to thistorque ratio by being accelerated faster than the. drive, causing hammerheads F to be turned or rockedin a clockwise direction (from theposition. of the operator using the wrench) and thus disrupting thedriving contact between hammer faces 23 of hammer heads F g and thecooperating anvil faces 35 of the driven The shank 37 of driven elementI revolves in 1 bearing 33 which serves as both a radial and' thrustbearing. At the extreme end of shank 31 of driven element I is anon-circular, preferably square portion 3,8 that receives theconventional socket or Wrench 39, rigidly mounted thereon in anysuitable manner. End portion 38, of course,

element I, and'the driven element remains at rest (Figs. 14 and 15).

After the disruption of the drive, driving element C, parts H, drivingconnections E, and rotatable torque receiving member D, all rotate aboutcentral shaft if for aninterval, during which, through the cooperativefunctions of the guides, (cylindrical surface 3 3. of driven element I,andtheinner cylindrical surface 55 of ring G acting on the rounded noses25 or arcuate' surface portion 28, respectively, of the hammer heads F),the driving connections are forced by the drive into potential drivingrelations (Figs. 12,13, 18'and 19). The said interval of drivingrequired to force the driving connection-s into potential drivingrelations depends on the design, application and type of driving power,and usually never exceeds (sixty-five degrees) of a revolution. Afterthe driving connections have been forced by the drive into potentialdriving relations, the driving element C, torque balancer D and hammerheads F allrotate as a unit until the hammer faces 23 of the hammerheads F, contact the anvil faces 35 of the driven element I, andsubstantially at this instant, an impact is delivered and the torquebalancer D is accelerated and the driving connection between the hammerfaces 23 and the anvil faces 35 then is disrupted as previouslydescribed.

The driven element I transmits the drive through its end portion 38 tothe conventional socket or wrench 39; which drives the head 'of the nut,bolt, or'other resisting element being turned, and impacts occur atsuccessive intervals until the bolt is suiliciently tightened, orotherwise turned, or the operator terminates the operation at any time.It is obvious from the foregoing that the driven element I is driven atthe same speed as the driving element C when the ratio of the drivingtorque to the resisting torque is substantially the same, and that whenthe resisting torque is greater thanthe driving torque, because of theresistance encountered, the driven element I is driven at intervals bysuccessive impacts and forces due to the acceleration of the rotatabletorque receivingmember D.

Fig. 12 shows the relative positions of the gear teeth 3! of parts H, tothe contacting surfaces l6 of the tooth spaces of 'the driving elementC, at the time of impact, or when the entire mechanism is being drivenas a whole with substantially no relative movement between the componentparts of the mechanism. Fig. 13 shows the corresponding relativepositions of the hammer faces 23 of driving connections E to the anvilfaces 35 of the'driven element I, and inner cylindrical surface 55 ofguide ring G at the same period as in Fig. 12. Here hammer faces 23 arein driving contact with the cooperating anvil faces 35 of the drivenelement I, rounded noses 25 of the hammer heads F are in contact withsurfaces 34 of the driven element I, being,

forced into this position by the driving force imparted through drivingelement C to gear teeth 3! of parts H. I

Fig. 14 shows the relative position of gear, teeth 3| of parts H totheir cooperative contacting surfaces |6 of the driving element 0, justafter im pact, or at, or near the beginning of the full disruption ofthe drive. r

Fig. 15 shows the relative position between hammer head F and drivenelement I at the same period as in Fig. 14, with hammer surfaces 23 ofhammer head F in contact with the cooperating anvil surfaces 35 atpractically one point. i

The angle made by the broken line OM in Fig. 14 and full line OPrepresents the angle through which the drivingelement C could haverotated from its impact position or driving position shown in Fig. 12.And the angle made by the vertical center line passing through center ofrotation O and the dot and dash line OS represents the minimum angle throtatable torque receiving member D could travel since the time ofimpact. It is obvious from the magnitude of these two angles, that therotatable torque receivin member D has rotated more than twice as fastas the driving element C, during the time that was required for thedriving element to rotate through the small angle MO-P. But thecomparison of the magnitude of these angles does not disclose themaximum acceleration of the rotatable torque receiving member D, sincemember D had begun to slow down before it reached its point of traveldisclosed in Figs. 14 and 15 and its acceleration was greater at theinstant of contact disclosed in Figures 12 and 13. This slowing down ofthe rotatable torque receiving member D will b more apparent in the nextstep of the operation disclosed inFigs. l6 and 17.

Fig. 16 shows the positions of the gear teeth 3| of parts H relative tocontacting surfaces l6 of the driving element C, at practically thepoint of total disruption of the drive. Fig. 17 shows the positions ofthe hammer heads F relative to the driven element C at the same periodas in Fig. 16. In the position shown in Fig. 16 the driving element Chas the maximum mechanical advantage to cause parts H to turn or rockthe driving connections E in their bearings 29 and 30 in rotatabletorque receiving member D, since the contacting surfaces I6 of drivingelement C, contact the teeth 3| of parts H at the farthest possiblepoints from the centers of parts H. The purpose of designing the toothto secure this condition is. that at this point in the operation,thedrive begins to force the driving connection E into potential drivingrelations which is accomplished by the turning or rocking parts H abouttheir own axis, which in turn rotate driving connections E and theirhammer heads F, such that the rounded noses 26 of hammer heads F aremoved to contact guiding surface 34 of the driven element I, or thearcuate surfaces 23 of the hammer heads F are moved to contact innecylindrical surface 55 of the guide ring G.

Fig. 17 discloses the hammer head-F of the driving connection E tiltedor rocked at its greatest possible angle about its own axis and inaclockwise direction, or at the point inits operation where it changesits direction of rotation or rocking and thereafter can rotate only in acounterclockwise direction about its own axis. At this point in theoperation, guide of hammer heads F may be'obtained from any one of threesurfaces, from rounded noses 25 of hammer heads F contacting the roundedapex of anvil surfaces 35 of driven element I, rounded noses 26 ofhammer heads F contacting cylindrical surface 34 of driven element I,and arcuate surface 28 of ham mer heads F by contacting innercylindrical surfaces 55 of guide ring G.

Fig. 16 shows the relative positions of gear teeth 3| of parts H to thecontacting surfaces [6 of the driving element C. It is obvious bycomparison of the relation of the parts disclosed in Figs. 16, 12 and 14relative to their rotation about the center of rotation of the drivingelement C, that the average speed of the rotatable torque receivingmember D (on which parts H and driving connection E aremounted) and thedriving element C have been almost the same between the twopoints'ofoperation represented by Figs. 14 and 16 and that the rotatable torquereceiving member D has slowed down to almost the speed of the drivingelement 0.

Fig. 18 shows the relative position of gear teeth 3| of parts H andcontacting surfaces is of driving element 0 after the total disruptionof the drive, and the driving connections are in normal potentialdriving positions. Fig. 19 shows hammer heads F at the same period as inFig. 18. -Rounded noses 25 of hammer heads F are now riding thecylindrical guiding surface 34 of driven element I, and arcuate surfaces21 of the hammer heads F arein sliding contact, or close to proxiinityof sliding contact, with'the inner cylindrical surface 55 of guide ringG. It is obvious from the relation of the parts disclosed in Figs. 18and 19 that at this point in the operation that the driving element 0and the rotatable torque'receiving member D are rotating at thesame'speed. The relative positions of the gear teeth 3| of parts H tothe contacting surfaces It of the driving elements C are the same inboth Figs. 12 and 18;

From the drawings, it will be seen that the device is readilyreversible, by reversing the direction of the power drive. When areversal of the drive is required, to secure smoothness of operation,hammer heads F should start to rotate first about their own axis, beforethe actual driving or rotation of the rotatable torque receiving memberD starts to rotate about the center of rotation of the driving elementC. This is accom-:

plished by designing the teeth 3| of parts H such that the maximummechanical advantage is had by the contacting surfaces of the toothspaces l of the driving element 0, with contact of the gear teeth 3| asfar from the center of rotation of the parts H as possible. As statedbefore, the

advantage of starting the rotation of parts H about their own axis, isto force as quickly as possible the driving connections into potentialdriving relation, and this is accomplished primarily by the rotation ofparts 1-1.

It should also be apparent from the foregoing description that therotatable torque receiving member D absorbs the reaction to the impactby its acceleration and this reaction is not transmitted to the housingor case of the impact wrench and thence to the operators hands. Forinstance, if the rotatable torque receiving member D were given a pushapplied at its periphery manually, or otherwise, to cause its rotationbefore driving contact with the driven element I was had, and thedriving connections E could turn in their bearings 29 and 3 3 in therotatable torque receiving member, that when the hammer faces 23 or 24of the hammer heads F contacted the cooperating anvil faces of thedriven element I, (assuming that the hammer heads F would be inpotential driving relation at the time of contact), rotatable torquereceiving member D would have to rotate faster than it was rotating atthe time of impact or contact to cause a disruption of the drive.

The angle made at the apex of the intersecting surfaces of the anvilportion 35, is a factor in determining the acceleration of the rotatabletorque receiving member D. If a constant speed of the driving element ishad, the smaller the said angle,

the greater the acceleration and the greater the impact.

In the slowing down of the rotatable torque receiving member D andgenerally stabilizing its rotation, the arcuate surfaces 21 and 28 ofthe hammer heads F, which are adapted to slidably contact the innersurface of guide ring G, function similarly to the damper mechanism usedin gasoline motor constructions to produce smooth performance. Thesearcuate surfaces 21 and 28 operate as a mild brake, until the instant ofimpact, when their contact with the inner cylindrical surface 55 ofguide ring G, is instantaneously broken. The rounded noses 25 and 26 ofthe hammer heads F, contacting the cylindrical surface 34 of the drivenelement I, function to some extent like the arcuate surfaces 21 and 28of the hammer heads F, sliding over the inner cylindrical surface ofguide ring G.

Since the speed of the motor, the mass of the rotatable torque receivingmember, and the angle made by the surfaces of the anvil faces 35 ingreat part determine the magnitude of the impact, and since all thesecan be varied to suit conditions, and since the rotatable torquereceiving member D is accelerated and there is no mass to be acceleratedagain to the motors speed after each impact, it will be apparent that acorrect relative prolportioning can readily be had of the vital parts,and hence that the impact wrench disclosed can be made for almost anytype of driving power, and satisfactory performance can be obtainedtherefrom.

Figs. 4, 5, 6 and 7 disclose a modification of the invention, in whichthe rotatable torque receiving member D is made in two parts 4| and 42.The object of this construction is to secure two bearings in therotatable torque receiving member D, for each driving connection E, suchthat the hammer heads F, integral with the driving connections E have abearing contiguous to each of their sides longitudinally along the shaftportions 2%), hammer heads F being located between the shaft ends 20, ofthe driving connections E. This construction is particularly desirablefor heavy duty wrenches.

Part 4| of rotatable torque receiving member D (Figs. 6 and 7) has anextending arcuate segment 43, portions of which function similarly tothe jaws of a jaw clutch and abut similar portions 44 of part 42 ofmember D. Arcuate lips d5 of portions 43 fit tight over arcuateprojections 45 of part 42 and locate the parts centrally. The parts 4|and 42 are press-fitted together and are further held in place by rods4! which extend through holes 48 of part 4| and holes 49 of part 42.Heads 59 of rods 41 (Figs. 5 and 6) contact part 42, and the other endsof rods 4'! each have an annular groove, into which fits a conventionalspring fastening ring 5| contacting part 4|. The parts 4| and 42 arethus held together as practically one solid part.

The driven element I is elongated comparably to driven element I of Fig.1 in order that part 42 of rotatable torque receiving member D mayrevolve about it. A bushing 52 (Figs. 4 and 6) is conventionally locatedin part 42 of rotatable torque receiving member D and functions as abearing between a portion of the driven element 1 and rotatable memberD.

Shaft portion II of driving element C, fits in hole IQ of part 4| of therotatable torque receiving member D, and the member D is free to rotateabout shaft portion l1.

Smaller shaft portion H5 in turn fits into cavity $5 of driven element 1which acts as a bearing for shaft portion I8. Shaft portions 23 ofdriving connections E fit into bearings 29 and 38, formed in rotatabletorque receiving member D, and are free to rotate thereon.

Hammer heads F are integral with driving connections E and are free tooperate in apertures of the rotatable torque receiving memher I), andthe hammer faces 23 and 24' (not shown) of the contacting heads F areadapted to contact anvil faces 35 of the driven element I through theseapertures 53.

Parts H are splined to shaft portions 28, and teeth 3|, operate in gearteeth spaces iii of driving element C exactly as in the form shown in Fi.1.

I claim:

1. In an impact tool in combination, a rotatable driving member, arotatable driven member having an impact receiving surface, a drivingconnection between said driving and driven members including a forcereceiving member rotatably mounted to rotate relative to said members, ahammer rotatably carried by said force receiving member and having animpact applying surface adapted torimpactlsaid receiving surface, saidimpact applying and impactreceiving surfacesat the time fof impact beingpositioned with respect to the axis of rotation of said hammer so thatalinenormal to their engaging surfaces at any point: of theentirefportion thereof passes in back of said axis ,with respect -to thedirection of rotation of ,the driving mem er whereby, when theforceKresisting movement of the driven member exceeds the force tendingto drive said driven member said force receiving member is moved fasterthan said driving member in the direction of rotation of the drivingmember and the hammer is rotated in one direction about its axis todisrupt its driving connection with said impact receiving surface, saiddriving connection also including means for causing said hammer torotate in the opposite direction when said driving connection has beendisrupted, said last mentioned means including a member operativelyconnected with said hammer and contacting a driving surface on saiddriving member, and guide means for controlling the extent of rotationof said hammer in said opposite direction to locate the impact applyingsurface thereon in a predetermined position relative to said impactreceiving surface.

2. In an impact tool, in combination, a rotatable driving member, arotatable driven member having an impact receiving surface, a drivingconnection between said driving and driven members including a rotatablymounted hammer'having an impact applying surface adapted to impact saidimpact receiving surface, said driving connection also including meansfor causing said hammer to rotate in the direction of rotation of thedriving member to disrupt said d'riving connection in response to theresultant component of force applied to said force applying surface atthe time of impact of said surfaces, when the force resisting movementof the driven member exceeds the force tending to drive said drivenmember, all lines normal to said impact applying surface, at the time ofimpact being posi tioned behind the axis of rotation of said hammer withrespect to the direction of rotation.

of said driving member.

3. In an impact tool, in combination, a rotatable driving member, arotatable driven member having an impact receiving surface, a drivingconnection between said driving and driven members including a rotatablymounted hammer having an impact applying surface adapted to impact saidimpact receiving surface, said driving connection also including meansfor causing said hammer to rotate in the direction of rotation of thedriving member to disrupt said driving connection in response to theresultant component of force applied to said force applying surface atthe time of impact of said surfaces, when the forceresisting movement ofthe driven'member exceeds the force tending to drive said driven member,all lines normalto said im-,

pact applying surface, at the time of impact being positioned behind theaxis of rotation of said hammer with respect to the direction ofrotation of said driving member, said driving connection also includingmeans for causing said hammer to rotate in the opposite direction tothat of the driving member, when said driving connection has beendisrupted, and guide means for controlling the extent of rotation ofsaid hammer in said opposite direction to locate the impact applyingsurface thereon in a predetermined position relative to saidimpactreceiving surface.

. .4. In an impact tool,'in combination, a rotatable driving -member, arotatable driven member having an impact receiving surface, a drivingconnection between said driving and driven members'comprising arotatably mounted hammer having'an impact applying surface adapted toimpact said impact'receivingsurface, said driving connection alsoincluding means for causing said hammer to rotate in the direction ofrotation of the driving member to disruptsaid driving connection inresponse to the resultant component of the force applied to said forceapplying surface at the time of impact of said surfaces, when the forceresisting movement of the driven member exceeds the force tending todrive said driven member, said driving connection also including meansfor causing said hammer to rotate in the opposite direction to that ofthe driving member when said driving connection has been disrupted andguide me'ans'including inner and outer cylindrical surfaces and in whichthe inner Q end of said impact applying surface is provided having animpact receiving surface, a driving force receiving member for rotationabout an with a rounded nose adapted to engage the inner' guide surfaceand in which the hammer is provided with a cylindrical surface adaptedto engage the outer guide surface.

5. In an impact'tool, in combination, a rotatable driving member, arotatable driven member connection between said driving and drivenmembers comprising a force receiving member rotatably mounted to moverelatively to said driving and driven members, a shaft mounted in saidforce receiving member for rotation about an axis spaced'radiallyoutward from theaxisof rotation of said force receiving member, a hammersecured to said shaft to rotate therewith and having an impact applyingsurface adapted to impact said impact receiving surface, all linesnormal to said impact applying surface at the time of impact beingpositioned behind the axis of rotation of said hammer with respect tothe direction of rotation of said driving member whereby the resultantcomponent of the force resisting movement of said driven member appliedto said impact applying surface at the time of impact, causes said forcereceiving member to be moved faster than the driving member and in thesame direction and said hammer is rotated in the same direction todisrupt said driving connection when the force resisting movement of thedriven member is greater than the driving force applied to the drivenmember.

6. In an impact tool, in combination, a rotatable driving member, arotatable driven member having an impact receiving surface, a drivingconnection between'said driving and driven members comprising a forcereceiving member rotattbly mounted to move relatively to said drivingand driven members, a shaft mounted in said axisspaced radially outwardfrom the axis of rotation of said force receiving member, a hammersecured to said shaft to rotate therewith and having an impact applyingsurface adapted to impact said impact receiving surface, all linesnormal to said'impact applying surface at the time of impact beingpositioned behind the axis of rotation of said hammer with respect tothe direction of rotation of said driving member, whereby the resultantcomponent of the force resisting movement of said driven member appliedto said impact applying surface at the time of impact,

11 causes said force receiving member to be moved faster than thedriving member and in the same direction and said hammer is rotated inthe same direction to disrupt said driving connection when the forceresisting movement of the driving memher is greater than the drivingforce applied to the driven member, said driving connection alsoincluding a member secured to said shaft and having a curved surfaceadapted to slidably en- 12 gage a radially extending surface on saiddriving member whereby said hammer is rotated in the opposite directionwhen said driving connection is disrupted and guide means forcontrolling the extent of rotation of said hammer in said oppositedirection to locate the impact applying surface thereon in apredetermined position relative to said impact receiving surface.

CARROLL H. RICHARDS.

